1. Field of the Invention
The present invention generally relates to an illumination system, and more particularly to a lens array which improves the optical efficiency of the illumination system and a method of forming an image on an output patch of the illumination system.
2. Description of the Related Art
Illumination systems are typically used with projection systems and provide light to projectors which project images and data on a screen for viewing. Generally, a light source is directed in one direction by a reflective collector which creates a light beam. This light beam may be directed by an integrator toward a semi-transparent medium such as a theatrical film or a light valve (liquid crystal display) which then projects an image or data. The image is then focused using a lens on a screen or other appropriate display device.
An exemplary conventional system is shown in FIG. 1, in which a light source 10 emits light beams 17. The light beams 17 are typically reflected by a collector 11 to integrator plates 12A and 12B. Then, the light beams 17 pass through converging lens 13 to a semi-transparent medium 14 to illuminate an image. Thereafter, light beams 17 are focused with a projection lens 15 and the image from the semi-transparent medium 14 is displayed on the screen 16.
The integrator plates 12A and 12B may be separately provided, discrete plates or may be integrally formed as one plate. The integrator plate(s) are typically referred to as "an integrator system" or "an integrator array". The integrator array is for creating a uniform illumination patch. An integrator system typically has two sets of lens plates each with an array of lenslets positioned thereon.
A primary characteristic of plate 12A is that it has multiple convex lenslets 18 facing the light source and a planar surface 19 on the opposite side. Plate 12B has a structure opposite that of plate 12A, and has a planar surface 20 on the side facing the light source and multiple convex lenslets 21 on the side opposite the light source. When plates 12A and 12B are combined into one plate, the two planar surfaces 19 and 20 are formed as one solid section.
The shape of the resulting output patch is determined by the shape of the lenslets on plate 12A. For example, if the desired output area has a rectangular shape, then each of the lenslets 18 on plate 12A is also rectangular. Further, these lenslets are arrayed such that the perimeters of all of the lenslets combined match the circular aperture of the collector 11 as closely as possible.
Lenslets on plate 12B are arrayed in a pattern identical to that on plate 12A. Then, the image of plate 12B is directed onto the aperture of the system. For example, in a projection system, plate 12B would be imaged into the circular aperture of the projection lens 15. Thus, it is generally preferable that the perimeter of the lenses on plate 12B be circular.
Each of the lenslets on an integrator array works in conjunction with a companion (e.g., corresponding) lenslet on the other array. The light path between any pair of corresponding lenslets is independent of the light path of any other pair of corresponding lenslets. Each of the lenslets 18 on plate 12A forms an image of the light source at the center of companion lenslets 21 on plate 12B. Each lenslet 21 on plate 12B, along with the converging lens 13, forms images from its companion lenslet on plate 12A at the semi-transparent medium 14.
However, in prior art systems the extent of the system is large because the size and arrangement of plate 12B is the same as the size and arrangement of plate 12A. "Extent" defines the size of the beam or the size of the corresponding optical system. The maximum usable extent of a projection system is limited by the size of the light valve and the aperture of the projection lens. If the extent of the illumination beam is greater than the extent of the projection system, some light will be lost.
Therefore, it is advantageous for a collection system to produce a light beam with an extent as small as possible to reduce power consumption and to reduce manufacturing costs associated with smaller projection systems. Hence, if a more narrow beam is desired (e.g., a smaller extent) in conventional systems, a large portion of the light is simply blocked and the efficiency of the system is reduced.
Further, the conventional systems are disadvantageous in that the first plate has the same size as the second plate. This creates problems of having the plates fit within a circular aperture and also increases optical extent.
Further, the conventional systems have the problem of center obscuration which wastes space and which has an increased extent.